10 February 2014
System that converts moving pictures and sounds
into electronic signals that can be broadcast at great distances.
The people behind the invention:
Vladimir Zworykin (1889-1982), a Soviet electronic engineer and
recipient of the National Medal of Science in 1967
Paul Gottlieb Nipkow (1860-1940), a German engineer and
Alan A. Campbell Swinton (1863-1930), a Scottish engineer and
Fellow of the Royal Society
Charles F. Jenkins (1867-1934), an American physicist, engineer,
The Persistence of Vision
In 1894, an American inventor, Charles F. Jenkins, described a
scheme for electrically transmitting moving pictures. Jenkins’s idea,
however, was only one in an already long tradition of theoretical
television systems. In 1842, for example, the English physicist Alexander
Bain had invented an automatic copying telegraph for sending
still pictures. Bain’s system scanned images line by line. Similarly,
the wide recognition of the persistence of vision—the mind’s
ability to retain a visual image for a short period of time after the image
has been removed—led to experiments with systems in which
the image to be projected was repeatedly scanned line by line. Rapid
scanning of images became the underlying principle of all television
systems, both electromechanical and all-electronic.
In 1884, a German inventor, Paul Gottlieb Nipkow, patented a
complete television system that utilized a mechanical sequential
scanning system and a photoelectric cell sensitized with selenium
for transmission. The selenium photoelectric cell converted the light
values of the image being scanned into electrical impulses to be
transmitted to a receiver where the process would be reversed. The
electrical impulses led to light of varying brightnesses being produced
and projected on to a rotating disk that was scanned to reproduce
the original image. If the system—that is, the transmitter and
the receiver—were in perfect synchronization and if the disk rotated
quickly enough, persistence of vision enabled the viewer to
see a complete image rather than a series of moving points of light.
For a television image to be projected onto a screen of reasonable
size and retain good quality and high resolution, any system employing
only thirty to one hundred lines (as early mechanical systems
did) is inadequate.A few systems were developed that utilized
two hundred or more lines, but the difficulties these presented
made the possibility of an all-electronic system increasingly attractive.
These difficulties were not generally recognized until the early
1930’s, when television began to move out of the laboratory and into
Interest in all-electronic television paralleled interest in mechanical
systems, but solutions to technical problems proved harder to
achieve. In 1908, a Scottish engineer, Alan A. Campbell Swinton,
proposed what was essentially an all-electronic television system.
Swinton theorized that the use of magnetically deflected cathode-ray
tubes for both the transmitter and receiver in a system was possible.
In 1911, Swinton formally presented his idea to the Röntgen
Society in London, but the technology available did not allow for
Zworykin’s Picture Tube
In 1923, Vladimir Zworykin, a Soviet electronic engineer working
for the Westinghouse Electric Corporation, filed a patent application
for the “iconoscope,” or television transmission tube. On
March 17, 1924, Zworykin applied for a patent for a two-way system.
The first cathode-ray tube receiver had a cathode, a modulating
grid, an anode, and a fluorescent screen.
Zworykin later admitted that the results were very poor and the
system, as shown, was still far removed from a practical television
system. Zworykin’s employers were so unimpressed that they admonished
him to forget television and work on something more
useful. Zworykin’s interest in television was thereafter confined to
his non working hours, as he spent the next year working on photographic
It was not until the late 1920’s that he was able to devote his full
attention to television. Ironically, Westinghouse had by then resumed
research in television, but Zworykin was not part of the
team. After he returned from a trip to France, where in 1928 he had
witnessed an exciting demonstration of an electrostatic tube, Westinghouse
indicated that it was not interested. This lack of corporate
support in Pittsburgh led Zworykin to approach the Radio Corporation
of America (RCA). According to reports, Zworykin demonstrated
his system to the Institute of Radio Engineers at Rochester,
New York, on November 18, 1929, claiming to have developed a
working picture tube, a tube that would revolutionize television development.
Finally, RCA recognized the potential.
The picture tube, or “kinescope,” developed by Zworykin changed
the history of television. Within a few years, mechanical systems
disappeared and television technology began to utilize systems
similar to Zworykin’s by use of cathode-ray tubes at both ends of
the system. At the transmitter, the image is focused upon a mosaic
screen composed of light-sensitive cells.A stream of electrons sweeps
the image, and each cell sends off an electric current pulse as it is hit
by the electrons, the light and shade of the focused image regulating
the amount of current.
This string of electrical impulses, after amplification and modification
into ultrahigh frequency wavelengths, is broadcast by antenna
to be picked up by any attuned receiver, where it is retransformed
into a moving picture in the cathode-ray tube receiver. The
cathode-ray tubes contain no moving parts, as the electron stream is
guided entirely by electric attraction.
Although both the iconoscope and the kinescope were far from
perfect when Zworykin initially demonstrated them, they set the
stage for all future television development.
Born in 1889, Vladimir Kosma Zworykin grew up in Murom,
a small town two hundred miles east of Moscow. His father ran
a riverboat service, and Zworykin sometimes helped him, but
his mind was on electricity, which he studied on his own while
aboard his father’s boats. In 1906, he entered the St. Petersburg
Institute of Technology, and there he became acquainted with
the idea of television through the work of Professor Boris von
Zworykin assisted Rosing in his attempts to transmit pictures
with a cathode-ray tube. He served with the Russian Signal
Corps during World War I, but then fled to the United States
after the Bolshevist Revolution. In 1920 he got a job at Westinghouse’s
research laboratory in Pittsburgh, helping develop radio
tubes and photoelectric cells. He became an American citizen
in 1924 and completed a doctorate at the University of
Pittsburgh in 1926. By then he had already demonstrated his
iconoscope and applied for a patent. Unable to interest Westinghouse
in his invention, he moved to the Radio Corporation
of America (RCA) in 1929, and later became director of its electronics
research laboratory. RCA’s president, David Sarnoff,
also a Russian immigrant, had faith in Zworykin and his ideas.
Before Zworykin retired in 1954, RCA had invested $50 million
Among the many awards Zworykin received for his culture changing
invention was the National Medal of Science, presented
by President Lyndon Johnson in 1966. Zworykin died on
his birthday in 1982
See also : Color television; Community antenna television; Communications
satellite; Fiber-optics; FM radio; Holography; Internet;
Radio; Talking motion pictures.